1. Field of the Invention
The present invention relates generally to valves having an expanding valve assembly, and more particularly but not by way of limitation, to an expanding valve which includes a valve closure member carrying one or more movable segments which move relative to the valve closure member to effect sealed closure of the valve.
2. Brief Description of the Prior Art
Valves with expanding gates have been taught in the prior art, wherein such valves comprise a gate having a female V-surface formed in the upstream side of the gate, a floating segment mounted on the gate, with a complementary male V-surface disposed thereon to engage and coact with the female V-surface on the gate. This gate assembly is usually positioned adjacent seating surfaces within the valve body to move transverse to the conduit axis (direction of fluid flow through the valve). Sealing during opening and closure is effected by the segment being wedged outwardly from the gate perpendicularly to the stem axis to effect sealing engagement with the seat faces. Examples of such valves are taught by U.S. Pat. No. 4,189,127 (Constantino); U.S. Pat. No. 4,530,488 (Kemp); U.S. Pat. No. 4,334,666 (Alvarez et al.); U.S. Pat. No. 4,341,369 (Meyer); U.S. Pat. No. 4,279,404 (Levin); U.S. Pat. No. 4,188,014 (Alvarez); U.S. Pat. No. 3,823,911 (Natho et al.); U.S. Pat. No. 4,188,016 (Whaley); U.S. Pat. No. 4,179,099 (Pierce, Jr.); U.S. Pat. No. 4,531,710 (Tort O.); U.S. Pat. No. 1,995,727 (Wetherbee); U.S. Pat. No. 556,006 (Fletcher); U.S. Pat. No. 1,521,531 (Trowe); U.S. Pat. No. 880,674 (Ladd); U.S. Pat. No. 4,405,113 (Erwin); Danish Patent 50,251 (Lindberg); and United Kingdom Patent 1,022,571.
In expanding valves of the type described, movement of the gate transverse to the conduit axis causes the floating segment to contact a stop structure which arrests further movement of the segment as the gate continues to move. The segment is thereby wedged outwardly so that it sealingly contacts the valve seat. This movement of the segment substantially perpendicularly to the stem axis is effected by the wedging action of the cooperating V-surfaces of the gate and segment.
The wedging action causing expanding movement of the segment occurs in the fully closed or the fully opened position of the valve, and, as indicated, results from predetermined, selectively located fixed segment stops interposed in the path of the segment as it moves with the gate. These segment stops arrest further movement of the segment in a direction parallel to the stem axis. When the gate is moved between the open and the closed positions, the segment is caused to collapse upon, or nest with, the gate as a result to the complementary interfitting V-surfaces.
For smooth and easy operation, and to avoid damage to the valve, it is important that the wedging action of the gate segment occur in only the open and/or closed positions, and that the segment remain in the collapsed condition when the gate is moving between the open and closed positions within the valve body. This prevents unnecessary dragging or binding of the gate assembly against the valve seats at a time when high integrity sealing is not required. Pre-expansion of the segment during travel, referred to as back-wedging, can require excessive torque on the stem to operate the valve, causing the valve assembly to jam, or twist-off and failure of the stem.
The Wetherbee patent (U.S. Pat. No. 1,995,727) is an early expanding valve for low pressure gas mains. A reciprocable gate is provided with a wedge member which coacts with inclined surfaces on the gate. The wedge member is carried by the gate and is caused to engage a shoulder stop to arrest its movement therebeyond, and further movement of the gate effects wedging, expanding movement of the gate assembly into its sealing position.
In the Erwin patent (U.S. Pat. No. 4,405,113), a complex expandable gate valve is disclosed having a first main stem which moves an entire multiple part gate as a unit in reciprocation upwardly and downwardly with respect to the fluid flow passageway, transversely across the valve body. The main stem has a coaxially aligned cam drive shaft having first and second oppositely threaded sections which function to respectively engage the main stem and a central gate block. The central gate block carries a plurality of cam surfaces thereon which are contiguous to each other, and which cooperate with seal blocks which also carry cooperating contiguous cam surfaces that interfit with the cam surfaces on the gate block. The seal blocks are moved outwardly as a result of movement of the central gate block, and the coaxial cam drive shaft is moved by rotation after the entire valve assembly has been positioned across the fluid flow passageway. The cam surfaces formed on the gate block consist of a plurality of contiguous saw-tooth indentations, or triangular steps, in the gate block which cooperate with complementary cam surfaces on the seal blocks. The complicated compound or dual stem structure disclosed in this patent is the mechanism by which the upper central gate block is caused to undergo a reciprocating up-and-down movement within a certain limited range previously established by movement of the main stream to set the gate into position within the valve body.
In the Erwin valve, the outer seal blocks will frequently ride upon, and bear primarily on, only one or at most two of the triangular camming surfaces for the reason that one of the camming surfaces is the highest, and projects out further than the others. This frequently occurs due to the difficulty of machining precisely identical mating saw-tooth surfaces over all of the gate that cooperates equally with all the seal block camming surfaces. The seal blocks consequently will frequently ride on, and bear primarily upon, only a single one of the camming surfaces. It is simply not possible, because of manufacturing tolerances, to predict which of the triangular wedge teeth will protrude out slightly further than the others. Thus, there will be an unpredictable rocking movement of the gate in relation to the seal block due to this very localized support.
The Over patent (U.K. 1,022,571) teaches an expanding valve assembly in which a rotatable valve spindle is connected to a tapered block on which are mounted two ball segments having complementary inclined inner surfaces wedgingly slidable on the tapered block. Each ball segment is forced into the sealing mode by the tapered block as a handle moves the valve spindle.
A spring-loaded detent is fitted to the hub of the handle. This detent cooperates with a vertical groove on the spindle. When the ball segments are free to move, the segments arie rotated by the spindle which in turn is rotated by the handle. Handle rotation is transmitted to the stem by means of the spring-loaded detent engaging the spindle. When the ball segments come to a stop after rotating 90 degrees, the detent becomes disengaged from the spindle groove. Further rotation of the handle reciprocates the spindle via a threaded connection between the handle and the spindle, while keeping the spindle non-rotational.
Resistance must be overcome at the sealing surface on the ball segments to rotate the ball segments. If this resistance at the ball segments is greater than the resistance offered by the detent spring, the spring-loaded detent will become disengaged. Such disengagement is unpredictable and can take place even at very low fluid pressure.